Apparatus for the grinding and/or dispersing of pigments in a liquid medium



July 25, 1967 J. H. J. woon 3,332,631

APPARATUS FOR THE GRINDING AND/OR DISPERSING OF PIGMENTS IN A LIQUID MEDIUM 2 Sheets-Sheet 1 Filed Nov. 9, 1964 ITFIIIII IH m 1) y 1967 J. H. J. wooo 3,332,631

APPARATUS FOR THE GRINDING AND/OH DISPERSING OF PIC'MBNTS IN A LIQUID MEDIUM 2 Sheets-Sheet 2 N wI United States Patent 3,332,631 AEPARATUS FOR THE GRINDING AND/0R DISPERSING 0F PIGMENTS IN A LIQUID MEDEUM Joseph Herbert James Wood, 52 Tybenliam Road, Merton Park, London, England Filed Nov. 9, 19-64, Ser. No. 409,745 Claims priority, application Great Britain, Nov. 27, 1963, 46,908/ 63 8 Claims. (Cl. 241-172) The present invention relates to an apparatus for grinding and/ or dispersing pigments in a liquid medium, for example in the manufacture of ink, paint or the like, in an apparatus in which grinding elements, such as rods, balls or cylinders and the material being treated are subjected to centrifugal force in a cylinder by means of a rotor provided with deflecting members which slide round the cylinder surface and successively part the elements from the cylinder surface against the opposing centrifugal force.

Such an apparatus is described and claimed in the specification of British Patent No. 848,514 and the invention further comprises improvements in or modifications of that apparatus to render it suitable for carrying out the method herein described and claimed.

The material to be treated may be fed from a hopper or force-fed in any suitable manner through an adjustable inlet to the cylinder so that under the action of the rotor it forms a film or layer on the cylinder surface.

The apparatus aforesaid has been found to be highly successful for treating materials of various kinds but considerable experimentation has shown that the efliciency of the apparatus can be much increased if certain features of construction and operation are observed.

The action of the rotor is to set up rotational flow of the material to be treated and rotation of the elements forming the grinding charge about their own axes while orbiting so that they have a rolling action on the film or layer of material while urged towards the cylinder.

surface and the deflecting elements by centrifugal force, the elements being parted from the cylinder surface by the deflecting members inwards towards the axis of the cylinder.

The present invention comprises an apparatus of the kind referred to for grinding and/ or dispersing pigments in a liquid medium in which the elements are cylindrical or spherical elements or substantially so to permit them to roll on the cylinder surface and on the deflecting members and the number of elements is such as to permit them to form a mono-layer extending over all said members and intervening cylinder spaces but less than the maximum number that could be accommodated as such a layer and such that the elements are free to approach and recede from one another in their orbit and undergo successive phases of deceleration and acceleration about their own axes both while they roll on the cylinder surface and while they are driven by the deflecting members. The diameter of the elements, the width of the deflecting members (i.e., from leading edge to trailing edge) and the distance between successive deflecting members on the one hand and the rotational speed of the rotor on the other hand are preferably such that the direction in which the elements rotate about their own axes is reversed both while they roll on the cylinder surface and while they are driven by the deflecting members and undergo successive phases of deceleration and acceleration about their own axes in their orbit.

To enable the elements to operate as aforesaid the number of elements employed should be chosen so that they form a mono-layer as aforesaid. The peripheral speed of the deflecting members, particularly as to the "ice inner element-deflecting faces of the said members, should be kept within certain limits. The mono-layer must be continuously maintained but too strong a pressure of the elements against the cylinder or deflecting elements must be avoided; hence the centrifugal forces set up in the elements should be kept within certain limits.

The number of elements present is of first importance as the presence of even one element in excess of the permissible number may interfere with the efliciency aimed at if it is not able to make contact with either the cylinder surface or the inner face of any deflecting element under the action of the centrifugal force or forces all the elements into pressure contact with one another or into such relation that they cannot approach and recede in relation to one another in operation.

It has been found that the relationship between the width of the deflecting members and the distance between successive deflecting members and the diameter of the elements is important to obtain the best result.

The elements may be spherical or be cylindrical rods or in the form of short cylinders, in which case the diameter referred to is the cross-sectional diameter. Preference is however had to the use of balls or of cylindrical rods extending substantially over the working length of the cylinder since there is a tendency for short cylinders not correctly to align. It has been found that the diameter of the elements, whether they be rods, balls or short cylinders, should preferably be from to /2". Diameters of less than are undesirable because the pressure they exert resulting from centrifugal force will usually be insufficient and in the case where the elements are rods extending over the whole or substantially the whole working length of the cylinder surface, they are liable by distortion not to preserve uniform line contact with the cylinder surface or the inner faces of the defleeting members. On the other hand if they exceed /2" diameter they will generally, with any suitable material such as steel used in their construction, be subjected to inertia effects to prevent the action desired. Optimum effects have so far been obtained where the elements are /8 in diameter. Particularly good results have been obtained where the elements are in the form of rods as aforesaid, in which case it is suitable to make them of steel. Straight cylindrical rods are also advantageous from the point of view of line contact and of simplicity in construction and assembly of the apparatus. It is considered that the optimum construction and disposition of the deflecting members are obtained when they are of substantially equal width and are spaced from one another by a distance substantially equal to their widths, although the width of each deflecting element may be up to 10% wider or up to 10% narrower than the said distance.

The aforesaid width of the deflecting members should be at least four times and preferably at least five times the diameter of the elements. It is advantageous that the width should be from eleven to sixteen times the said diameter and particularly good results have been obtained where the width is eleven or twelve times such diameter.

Thus good results have been obtained where the diameter of the cylinder surface is 3 /2 and eight deflecting members of about 0.028" in thickness are provided of a width of equally spaced around the cylinder; we found that 84 rods could be accommodated as a monolayer in this apparatus and that we obtained good results when 82 rods were in fact provided. I also obtained good results where four deflecting members of 1%" width were used in apparatus of otherwise the same size and again the number of elements which could be accommodated was reduced by one or more. I have also obtained .good

results with apparatus where the diameter of the cylinder surface was 12" and twelve deflecting members of 0.056 in thickness and of about 1 /2" in width were provided and When approximately 287 rods could be accommodated and 280 rods were found suitable according to the invention.

The peripheral speed of the deflecting members should be kept within certain limits, and it has been found that in the instances just referred to a peripheral speed of from 15 to 45 feet/second and advantageously of the order of 18 to 32 feet/ second is particularly suitable. The speed of the rotor must be suflicient to maintain the elements as a mono-layer but should not be such as unduly to increase the pressure of the elements against the cylinder surface or the deflecting members.

I have found it particularly advantageous to employ deflecting members in the form of rectangular blades of a thickness of at least .024", e.g., with a leading edge bevelled to an acute angle so that one face of the bevel follows or is substantially tangential to the cylinder surface and the other face is such as to enable a smooth pickup of the elements off the cylinder and with a trailing edge which may be blunt and straight or rounded, or even also bevelled if desired, and which also contacts the cylinder surface, so that the blades will make a chord with the cylinder surface and so that the forward edge of the blades will positively shear or doctor the elements and the material under treatment from the inner surface of the cylinder.

The alternating decelerating and accelerating motion imparted to the elements whilst rolling in contact with both the inner faces of the blades and the intervening regions of the cylinder surface results in shear action accompanied by gentle rolling pressure on the film of material by a high number of individual elements giving an infinitely variable action and a particularly high shear to pressure ratio and resulting as it were in multiple grinding hips in an apparatus the working diameter of which is small.

It is advantageous to assist the removal of the film of material from the discharge end of the cylinder and to this end the rotor may be provided with a wiper or scraper disposed to wipe or scrape the cylinder surface beyond the corresponding edges of the blades or between the blades and if desired beyond them. The wiper or scraper may be radially disposed or presented at a suitable angle to the cylinder. If the material is not positively ejected, material tends to build up the film thickness particularly at the outlet end where it should be thinnest.

It is desirable when setting the apparatus in operation and first orientating the elements as a monolayer, to increase the speed of rotation steadily and this may be achieved by providing the apparatus with a driving friction clutch which can be progressively engaged.

Such a clutch also serves for allowing the speed of the rotor to be controlled for the purpose of cleaning the apparatus. For this purpose a suitable solvent can be introduced and the speed so chosen that the grinding elements which will have collected in the bottom of the annular chamber between the rotor and the cylinder when the apparatus has been brought to a standstill can be car ried round through a certain angle to form a collective group and accompanied by a cascading or tumbling action and by so doing sweep the rotor surface clean.

The pressure or gravity feed of the material into the valve-controlled end passage may be from a suitable hopper or otherwise, and the pressure may be kept constant, e.g., by a suitable metering control of the head or by pumping the material to be treated.

In order that the invention may be the more clearly understood, reference is hereinafter made to the accompanying drawings in which FIG. 1 is a sectional elevation of one form of apparatus fltiwrding to the invention by way of example; FIG. 2

is an illustration of the manner in which the elements are decelerated and accelerated; and FIG. 3 is a detail View of the scraper means. FIGS. 4 and 5 are further detail views.

The apparatus comprises a cylinder 1, the operative surface being a hardened surface marked 2. The cylinder is located in a casing 3 providing an annulus 4, for heating or cooling fluid, the temperature of which can be checked by gauge 5. The rotor 6 is formed with radially flanged ends 7 which are peripherally notched or grooved at 7a to receive the ends of the deflecting members 8 (see also FIG. 2), so that these members are carried round with the rotor.

The deflecting members act like ploughs in that they part the grinding elements from the cylinder and take over control of the motion of the elements and in fact in the illustrated case they are of blade form; hence the terms deflecting member, blade and plough used herein are interchangeable. The ploughs are loosely mounted in relation to the rotor in the end grooves. They preferably have end tongues 7b (FIGS. 4 and 5) for engagement with the said grooves and are preferably of a length (excluding the tongues) approximately equal to the distance between the rotor flanges.

An annular chamber 9 is formed between the periphery 9a of the rotor and the inner surface 2 of the cylinder and the ploughs are disposed so that their leading ends 10 and trailing ends 11 (FIGS. 2 and 4) can engage the cylinder surface 2, the leading edge of each plough being bevelled to a sharp angle and the trailing end being left blunt and the ploughs being chordally arranged in relation to the cylinder surface.

The shaft 12 of the rotor is rotatably supported in bearings 13 in the end of the casing.

A valve 14 cooperating with the seating 15 is urged towards its seating by a helical compression spring 15a bearing at one end on the valve and at the other on a bush or thimble 16 screwed to the end of the shaft. This valve can be adjusted by a calibrated hand wheel 17 through micro-screw adjustment to vary the width of the ring shaped passage which is provided between the valve and its seating when the valve is opened, and the adjustment may be fixed by a lock nut 17a.

The liquid material to be treated will be fed through the inlet 18, e.g., from a siutable hopper and under a head which may be regulatable and if desired kept constant.

The material being treated will be in the form of a film or layer on the cylinder surface 2 and treated material is scraped off the cylinder at the end remote from the inlet by a scraper or wiper blade 19 carried by the rotor and rotating with the rotor (see FIG. 3) with its scraping or Wiping edge trailing. Alternatively a radial blade 19a could be provided. The material outlet is indicated by 20. i

The rotor shaft is suitably coupled or geared to a prime mover, e.g., electric motor and it is rotated at such a speed that the inner surfaces of the ploughs will rotate at an average peripheral speed of from 15 to 45 feet per second. With a cylinder surface 2 of a diameter of 3 /2 inches, a shaft speed of 1440 rpm. was found suitable, using eighty-two /s" diameter steel rods and eight ploughs of ,5 width as aforesaid and of a thickness of .028", said peripheral speed being then approximately 22 feet per second.

If in the 3 /2" cylinder apparatus aforesaid there are four equally spaced ploughs each of 1%" width and rods of 4; diameter were again used we found that greater throughput could be obtained and/ or less power needed than with the eight-plough apparatus and it has been found that as the number of ploughs used rises to say sixteen, the desired reversal of the direction of rotation of the elements does not occur and the effectiveness is greatly reduced. If the rods be of /s diameter the ploughs should in general never be less than /2" in Width and from 1" to 1% "is very suitable.

With the larger apparatus before referred to having a cylinder surface of 12" in diameter and twelve ploughs of 1 /2" in width and .056 thickness, successful results were obtained with the rotor rotating at 600 rpm, giving a peripheral speed of the ploughs of 31.4 feet/second; using 280 rods of V8" diameter.

The rotor speed in r.p.m. of course varies considerably with the diameter of the cylinder surface and it is important that the speed be chosen so that centrifugal force on the elements should be kept within certain limits. In making comparisons for different diameter cylinders simple calculations on the basis v /r can be made assuming the weight to be a constant and it is desirable that the speeds be chosen so that the centrifugal force calculated on this basis lies within the region of from 1500 to 4500 units. This force must be suflicient to keep the elements in eflicient rolling contact with the cylinder surface and the ploughs.

The operation of the apparatus will be understood from FIG. 2. The grinding elements are present in such a number that when centrifuged by the rotor they form a mono-layer such that the elements can all roll on the surface 2 or on the deflecting blades 8 and approach or recede from one another in the layer, i.e., the elements do not press one against the other around the series or at any rate only contact one another under pressure at certain regions.

The direction of rotation of the rotor and blades is indicated by the arrow B and the flow of the grinding charge by the arrow A. The elements are at any one time in groups contacting the cylinder directly and the ploughs respectively. Those contacting the cylinder surface tend to be rotated in the direction of the arrows C about their own axes, and those so marked are actually rotated in that direction. The action of the blades is for their leading edges to part the elements from the cylinder surface, see the elements marked E1. The blades now take over the drive of the elements and in consequence the elements are decelerated in their rotation about their own axes (elements E2, E3) and eventually this direction of rotation is reversed and the elements are accelerated in rotation about their own axes, see the elements E4, E5 and E6. The elements approaching and leaving the trailing ends of the blades make impact with one another and leave the blades and contact the cylinder (save for the presence of the liquid film) whilst still rotating in the same direction. Again a decelerating action occurs (elements C C C and eventually the elements whilst still contacting the cylinder are reversed as to their direction of rotation about their own axes and accelerated to the point where they are again parted from the cylinder surface by the next plough.

I have referred to balls and small cylinders, which may be of a synthetic or non-metallic material, e.g., steatite, or metal, e.g., steel, but flint pebbles or the like if carefully selected of suitable rounded form will suflice.

What I claim is:

1. Apparatus for grinding and/or dispersing pigments in a liquid vehicle, comprising:

a cylinder,

.a rotor and a multiplicity of rolling elements in said cylinder,

an inlet for the material to be treated in said cylinder and an outlet from said cylinder,

means for rotating said rotor for bringing said material into film or layer form on the cylinder surface and for centrifuging the said rolling elements to work on the said material,

deflecting members carried by the rotor and extending lengthwise of the rotor and arranged to move around the cylinder surface during rotation of the rotor for the purpose of parting the elements and the material from the cylinder surface,

said deflecting members being formed with scraping edges adapted and arranged to make scraping contact with the cylinder surface during rotation of the rotor,

means for supporting the deflecting members movably in relation to the rotor so that they are urged during rotation of the rotor against the cylinder surface to maintain scraping contact of their said scraping edges with the said surface; and

the number of said rolling elements is such as to permit them to form a mono-layer extending over all said deflecting members and intervening spaces of the cylinder and is less than the number which could be accommodated by such a layer.

2. Apparatus according to claim 1 wherein the said rolling elements are cylindrical rods of a length such as to extend over substantially the whole length of the individual scraping edges.

3. Apparatus according to claim 1 wherein the said deflecting members are each formed to have two spaced locations of contact with the cylinder surface in a direction lengthwise of the cylinder, one location of which is provided by a said scraping edge.

4. Apparatus according to claim 1 wherein the deflecting members are disposed with the outer faces chordally arranged in relation to the cylinder.

5. Apparatus according to claim l'wherein the deflecting members, from their leading edge to trailing edge in the direction of rotation are not more than 10% wider or less than 10% narrower than the width of the spaces between them.

6. Apparatus according to claim 2 wherein the diameter of said cylindrical rods is not less than or more than /2" and the width of the deflecting members is at least six times the diameter of the elements.

7. Apparatus according to claim 2 wherein the deflecting members have tongues at their ends which loosely engage grooves or slots in end flanges of the rotor and the length of the deflecting members, without the tongues, and of the said rods is approximately equal to the distance between the rotor flanges.

8. Apparatus according to claim 1 including scraper means on the rotor adjacent said outlet for assisting in the removal of the treated film or layer of material from the cylinder surface.

References Cited UNITED STATES PATENTS 639,406 12/1899 Kreiss 241-172 X 2,592,994 4/1952 Ahlmann 24l172 X 3,018,059 1/1962 Lodige 241-172 X FOREIGN PATENTS 1,289,073 2/ 1962 France.

62,756 6/ 1892 Germany.

848,514 9/1960 Great Britain.

WILLIAM W. DYER, JR., Primary Examiner.

HARRY F. PEPPER, JR., Examiner. 

1. APPARATUS FOR GRINDING AND/OR DISPENSING PIGMENTS IN A LIQUID VEHICLE, COMPRISING: A CYLINDER, A ROTOR AND A MULTIPLICITY OF ROLLING ELEMENTS IN SAID CYLINDER, AN INLET FOR THE MATERIAL TO BE TREATED IN SAID CYLINDER AND AN OUTLET FROM SAID CYLINDER, MEANS FOR ROTATING SAID ROTOR FOR BRINGING SAID MATERIAL INTO FILM OR LAYER FORM ON THE CYLINDER SURFACE AND FOR CENTRIFUGING THE SAID ROLLING ELEMENTS TO WORK ON THE SAID MATERIAL, DEFLECTING MEMBERS CARRIED BY THE ROTOR AND EXTENDING LENGTHWISE OF THE ROTOR AND ARRANGED TO MOVE AROUND THE CYLINDER SURFACE DURING ROTATION OF THE ROTOR FOR THE PURPOSE OF PARTING THE ELEMENTS AND THE MATERIAL FROM THE CYLINDER SURFACE, SAID DEFLECTING MEMBERS BEING FORMED WITH SCRAPING EDGES ADAPTED AND ARRANGED TO MAKE SCRAPING CONTACT WITH THE CYLINDER SURFACE DURING ROTATION OF THE ROTOR, MEANS FOR SUPPORTING THE DEFLECTING MEMBERS MOVABLY IN RELATION OF THE ROTOR SO THAT THEY ARE URGED DURING ROTATION OF THE ROTOR AGAINST THE CYLINDER SURFACE TO MAINTAIN SCRAPING CONTACT OF THEIR SAID SCRAPING EDGES WITH THE SAID SURFACE; AND 